Microwave switching tubes



March 25, 1958 w. E. COHAN ETAL MICROWAVE SWITCHING TUBES Filed April 30, 1953 Fig. l.

QUARTZ WOOL QUARTZ TAPE full; I

I INVENTORS William E. Cohan and ErnYesi A. Goldman ATTORNEY WITNESSES: 52,4 '4.

MICROWAVE swrrcmNG TUBES William E. Cohan, North Weymouth, Mass., and Ernest A. Goldman, Bloomfield, N. 3., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application April 39, 1953, Serial No. 352,130

Claims. (Cl. 315-39) -Our invention relates to microwave switching tubes, and, more particularly, to the use of woven quartz fiber tape near the input window of microwave gas switching tubes;

In accordance with the prior art, of which we are aware, gas switching tubes have been provided in radar apparatus, such as the devices which are commonly called transmit-receive tubes (TR tubes) or anti and transmitreceive tubes (ATR tubes) and which act to pass microwave oscillations during one portion of a radar pulse cycle and to prevent passage of such oscillations during another portion of that cycle. Tubes of this type usually comprise a rectangular, hollow box having walls of electrically conducting material. in the case of the TR tube, a window is provided in each end of the tube for admitting electromagnetic oscillations, or allowing those oscillations to leave the tube. In the interior of the TR tube there are provided two electrodes or cones which are oppositely disposed and extend inward toward the center of the tube. These two cones are provided in order to minimize leakage power and to some extent for producing a gas discharge therebetween. The gas discharge across the cone gap between the cones changes the characteristics of the tube so that it becomes no longer resonant at the frequency of the oscillations a plied thereto.

When oscillations of small amplitude enter the tube, such as those oscillations which are received as echoes from the target, the oscillations pass through the tube without causing a gas discharge to occur across the cone gap. On the other hand, when high power oscillations pass into the tube, when the tube is transmitting, these oscillations cause a breakdown in the tube which changes its characteristics so that the'tube prevents the passage of those oscillations.

The anti-transmit-receive or ATR tube comprises a cavity resonator with a single resonant window, both tuned essentially to the transmitted frequency. Under high power excitation a gas discharge in the region of the window effectively isolates the cavity resonator from the waveguide leading from the transmitter to the antenna, thus allowing low loss transmission. However, during low power excitation, the ATR cavity reflects an open circuit to the waveguide at the junction with the TR tube. This prevents loss of power into the transmitter branch of the waveguide, allowing the full received signal to go to the receiver.

When the oscillations of low amplitude which are refiected from a distant object, as an echo signal, encounter a TR switch or an ATR switch after a discharge has occurred, they are likely to meet with undesired interference due to the presence of residual electrons in the region. It is, therefore, necessary that these residual electrons be dispersed as rapidly as possible. The time required for the residual electrons to be cleared from the tube sufficiently to allow the weak received signals to pass through the tube is usually referred to as the recovery time of the tube.

2,828,442 Patented Mar. 25, 1958 In accordance with the prior art, of which we are aware, several attempts have been made at lessening the time required for recovery of gas switching tubes.

. Various different types of gases have been tried which aid in the elimination of the free electrons from the region. Another, and what appears to be a better solution has been the use of quartz wool placed inside the tube between the electrodes and the window. The quartz wool adsorbs the free electrons after the discharge has stopped, thereby accelerating the recovery of the tube. However, it has been found that quartz wool fibers in contact with the window are the cause of greatly increased rates of sputtering of metal from the tube wall or window frame across the glass of the input window. This sputtering has been found in some cases to eventually cause window failure by destruction of the vacuum seal. Sputtering may also result in the gradual deteriora tion of such tube characteristics as low level insertion loss in case of TR tubes or tuning susceptance in the case of anti TR tubes. Further, during tube assembly, in some cases it has been found that some of the quartz wool fibers will tend to protrude into the vacuum solder joint around the window. Since the solder does not wet the quartz fibers, there is considerable danger of producing leaky joints. High tube shrinkage may be expected unless extreme care is exercised in placing the quartz wool fibers in the tube.

It is accordingly an object of our invention to provide a microwave switching tube in which sputtering does not occur.

Another object of our invention is to provide a gas switching tube, wherein the quartz wool fibers will not be allowed to protrude into the vacuum solder joint around the window.

Another object of our invention is to produce a gas switching tube, the assembly of which is facilitated by an improved construction.

An ancillary object of our invention is to provide an improved gas switching tube for usewith microwave oscillations.

Another ancillary object of our invention is to provide a new and useful electrical apparatus.

The novel features which we consider characteristic of our invention are set forth with more particularity in the appended claims. The invention, however, with respect to both the organization and the operation thereof, together with other objects and advantages may be best understood from the following description of specific embodiments when read in connection with the accompanying drawing, in which:

Figure 1 is a showing in cross section of an ATR tube built in accordance with one embodiment of our invention, wherein the quartz tape is held in place by glue.

Fig. 2 is a showing in cross section of a TR tube built in accordance with another embodiment of our invention, wherein the quartz tape is held in place by the pressure of quartz wool thereon.

In accordance with our invention we provide a rectangular chamber 4 which is hollow inside and has walls of electrically conducting material. Boxes of this type are well known in the art as cavity resonators and are used in devices known in the art as microwave gas switching devices or, more particularly, as TR boxes or ATR boxes. Inside the TR box shown in Fig. 2 are provided two oppositely disposed electrodes 6, 8. The electrodes 6, 8 are provided for producing a gas discharge therebetween when oscillations of high power level enter the cavity. At one end of the TR box there is a window assembly comprising an end plate which may consist of the nickel, iron cobalt alloy described in Scott Patent 2,062,335. The end plate has a window 10 therein which has thereacross it a covering of material, such as glass, which is relatively transparent to microwave oscillations. The window 10 is provided in order to allow microwave oscillations to enter the cavity resonator 4. In the case of a TR tube, two windows are provided, in which case one end of the cavity resonator 4 is connected to a waveguide which is connected to the antenna and the other end of the cavity is connected toward a waveguide leading toward the receiving crystal. In the case of the ATR tube, shown in Fig. 1, the single window is connected to a waveguide connecting the transmitter with the antenna. A shorting plate 13 of conductive material is provided within the body 4 in Fig. 1 at a distance of approximately one quarter wavelength from the window 10. The effective cavity resonator volume is within the body 4 between the window 10 and the shorting plate 13. The body 4 extends beyond the short circuiting plate 13 and is sealed off at the end thereof. An aperture is provided in the plate 1.3 to permit evacuation of the cavity. The extension of the body 4 provides ease in evacuation or a gas reservoir if gas filled.

In accordance with one embodiment of our invention, we employ a blanket 12 cut from an insulating or dielectric tape such as woven quartz tape, which is commonly sold on the market under the trademark. Refrasil. This blanket or tape 12 of woven quartz in the embodiment, shown in Fig. 2, is placed on top of a wad 14 of quartz wool that fills the cavity inthe region between the input window 10 and the electrodes 6, 8. The blanket or tape 12 is of rectangular shape and its size is slightly smaller than the cross-sectional dimensions of the metallic box 4 forming the tube body. Thus direct contact in a disorderly pattern between quartz wool fibers and the window is avoided. Instead there is provided the relatively uniform contact of a piece of woven quartz cloth, which does not have extraneous fibers which would extend into the solder joint between the window 10 and the body 4 f the tube.

In the embodiment, shown in Fig. l, the tape 12 made of quartz fiber is glued to the end of the tube against the window 10. It has been found that since the main discharge of an ATR tube occurs directly behind the input window and is only a few mils thick, the recovery agent (Refrasil quartz tape) has to be flush with the window. In some circumstances it has been found that the pressure of the quartz fluff or wool 14 on the tape 12 is not sufficient to hold the tape tightly in place. Furthermore, the reduction in resonant frequency due to the increase in capacitance resulting from the mass of quartz wool used may be undesirable. It is, therefore, suggested in the preferred embodiment of our invention that the Refrasil tape be cemented to the back of the input window 10.

The following method of assembly is suggested:

After the Kovar glass window assembly has been completed, the Refrasil quartz tape 12 should be ccmented to the window at the extreme edges so that the cement will be out of the discharge area. The tape 12 is thus positioned flush with the window and thereby accomplishes its prime function. The capacity effect of the quartz fluff is eliminated and also any additional arc loss which might otherwise be produced by the fluff will be avoided.

It is believed that a large number of cements well known in the art will be useful in cementing this tape to the window. In our tests we have used a cement of sodium silicate. This cement is very effective when the input Window is soft soldered in place since the sodium silicate is heat resistant to 300 C. For hard soldered tubes we have successfully employed a cement consisting of a low melting glass powder, such as Corning code No. 7570.

Although we have shown and described specific embodiments of our invention, we are aware that other modifications thereof are possible. Our invention, therefore, is not to be restricted except insofar as is necessitated by the prior art and the spirit of the invention.

We claim as our invention:

1. A microwave gas switching tube comprising walls of electrically conducting material defining a cavity, a pair of electrodes extending into said cavity so as to oppose each other, a window of dielectric material provided in a wall of said cavity, and a layer of fibered insulating tape attached to said window.

2. A microwave switching tube comprising a hollow box having walls of electrically conducting material, said box having windows in the ends thereof of dielectric material for allowing microwave oscillations to enter and leave said box, a pair of oppositely disposed electrodes extending into the interior of said box for producing a.

4. In combination, a cavity resonator, a window trans-, parent to microwave oscillations in one end of said resonator, and a piece of insulating fiber tape adjacentsaid' window inside said resonator.

5. In combination, a cavity resonator, a pair of. op-.

positely disposed electrodes extending into the interior of said resonator, a window transparent to microwave oscillations in one end of said resonator, and a layer of.

dielectric fiber tape adjacent said window inside said. resonator.

References Cited in the tile of this patent UNITED STATES PATENTS 2,422,190 Fiske June 17,194? 2,471,128 Stein May 24, 1949 2,496,865 Fiske Feb. 7, 1950- 

